The disclosed embodiments relate to a thrust reverser to form a reverse flow from a secondary thrust flow in a double-flow nacelle. The disclosed embodiments also relate to a nacelle for a double-flow engine equipped with such a reverser for aircraft.
In general, the nacelle has a cowling in which there is an engine. Air is drawn into the nacelle at a front extremity of said nacelle, located at the forward part of the aircraft. The nacelle ejects the absorbed air at high velocity toward the rear of the aircraft. To permit forward motion of the aircraft, it is necessary for the air mass passing through the nacelle to have a discharge velocity higher than the intake velocity. The discharge velocity of the air mass is increased by a known method inside the nacelle.
The air passing through the nacelle is composed of two different flows. A first flow, called the primary flow, passes through the engine. The primary flow is ejected directly out of the nacelle from the rear of the engine. A second flow, called the secondary flow, passes through an air passage channel before being ejected out of the nacelle. This air passage channel is an annular channel formed between an inside wall of the nacelle cowling and an outside wall of the engine, and extends along said engine.
When the aircraft lands, mechanical brakes provide for mechanical braking of said aircraft. However, once the aircraft is on the ground it is known how to utilize thrust reversers in addition to the mechanical brakes. The thrust reversers in particular favor reducing the landing distance of the aircraft. The landing distance of the aircraft means the distance traveled by the aircraft between the moment the landing gear of the aircraft touches the runway and the moment when the aircraft has completely stopped on the runway. The thrust reversers deflect all or part of the air flow ejected from the rear of the nacelle and eject it toward the front of the aircraft. The reversers thus create an aerodynamic drag and accordingly a braking force called the “counterthrust,” which contributes to the slowing of the aircraft.
Thrust reversers with two pivoting doors made in the thickness of the nacelle cowling are known as thrust reversers. The doors are distributed over an outer circumference of the nacelle cowling. The number of reversers may vary, depending on the particular applications, and according to the method of mounting the propulsion apparatus assembly on the aircraft. In the inactive position the doors are closed, in other words they extend in an extension of the cowling. In the active position, the doors are open. A displacement of the doors is such that parts of the doors then extend toward the outside of the nacelle in a direction essentially perpendicular to a longitudinal axis of the nacelle. Generally speaking, each of the two doors has a free extremity and a pivoting extremity. By a free extremity is meant the extremity of the door that describes motion in an arc when the door is displaced from the closed position to the open position. By a pivoting extremity is meant the extremity of the door on which the pivoting axis is positioned. Thus, when the doors are open, the free extremity of one of the two doors extends toward the interior of the nacelle, thus at least partially blocking the air passage channel. The flow of air is then blocked, and is evacuated to outside the nacelle by an opening made by opening the second door toward the outside of the nacelle, which deflects the flow of air toward the front of the nacelle so as to produce a thrust reversal.
The document FR 2 887 225 discloses a nacelle equipped with thrust reversers. Each thrust reverser is equipped with an internal door and an external door, with each of these doors having a unique direction of displacement. These two directions of displacement are opposed, so that when the thrust reverser is in the active position, the external door sends the air flow blocked by the internal door inside the nacelle, toward the front of the nacelle. Locking mechanisms are provided to guarantee that no untimely opening of the doors can occur while the aircraft is in flight.
One of the problems of the known reversers is the complexity of the movable elements that constitute the door displacement apparatus, so that there is a risk of more frequent failure. Furthermore, these movable elements are arranged relative to the door in such a manner that a portion of these elements is situated outside the cowling of the nacelle, inducing aerodynamic perturbations at the nacelle.
The thrust reversers with pivoting doors are also questionable in principle since they can be opened in an untimely manner. Actually, the secondary flow passes under pressure into the air passage made between the inside wall of the cowling and the outside wall of the engine. Also, the secondary flow exerts pressure against the inside wall of the cowling and accordingly also on the doors. Since the displacement of the doors is directed toward the outside of the nacelle, the force exerted by the flow of air against the inside wall of the cowling favors the opening of the doors. The risk of untimely opening is all the greater when the control mechanism fails. A locking apparatus is generally proposed to block the doors while the airplane is in flight. However, such an apparatus does not guarantee for certain the closing of the doors; actually it can also become inoperative itself during flight, and this supplementary apparatus also causes an increase in the cost of manufacture and also in the weight of the nacelle equipped with such a reverser.
In general, the currently proposed thrust reversers are associated with burdensome maintenance and design constraints linked to the risk of untimely opening in flight.